Yes, I have multiple gcc version installed but during compilation only gcc command is used and I symlinked it to gcc-4.6.
I do have these flags so I don't know... I have Makefile and Makefile.Release; the latter seems to be some Windows specific stuff but Makefile should be fine from n900 perspective.

Update - 20181127://I only managed to step through the arm_neon problem when I disabled that part of the code in CameraThread.cpp that was using arm_neon.h. In this way fcamera was built successfully but does not work either - starting from command line it says that it cannot initiate the thread that is responsible for the "live image" through the camera... And also has some glib warnings.
My knowledge is way far from the point where I could tell that "I can investigate it" so I leave it as is.